(1) Field of the Invention
The present invention generally relates to a malfunction detection apparatus for an evaporated fuel purge system in an internal combustion engine, and more particularly to an apparatus for detecting a malfunction in an evaporated fuel purge system which is provided in an internal combustion engine for purging an evaporated fuel or fuel vapor into an intake system of the internal combustion engine under given operating conditions and for adsorbing the fuel vapor in an adsorbent in a canister, so that an air-fuel mixture is fed into a combustion chamber in the internal combustion engine.
(2) Description of the Related Art
An evaporated fuel purge system is provided in an internal combustion engine for adsorbing an evaporated fuel or fuel vapor, evaporated in a fuel tank, temporarily in an adsorbent in a canister so as to prevent the fuel vapor from escaping to the atmosphere, and for purging the adsorbed fuel vapor in the canister into an intake passage of the engine during engine operation. This evaporated fuel purge system usually includes a vapor passage connecting the fuel tank to the canister and a purge passage connecting the canister to the intake system of the engine. Also, a purge control valve is provided at an intermediate portion in the purge passage. However, in a case in which the vapor passage is damaged or a connecting pipe in the vapor passage is separated due to a certain problem, the fuel vapor may escape to the atmosphere from the evaporated fuel purge system.
A conventional malfunction detection apparatus for detecting a malfunction in the evaporated fuel purge system is known. For example, Japanese Laid-Open Patent Application No.2-130255 discloses such a malfunction detection apparatus. In this conventional malfunction detection apparatus, a pressure sensor is provided in the purge passage between the canister and the purge control valve for outputting a signal indicative of pressure in the purge passage, and a malfunction in the evaporated fuel purge system is detected by the malfunction detection apparatus in response to an output signal of the pressure sensor. The malfunctions thus detected include a clogging of an air inlet of the canister, a problem in the purge control valve, a clogging of the purge passage, and a pipe separation therein. However, pressure in the vapor passage between the fuel tank and the canister is not detected by such a conventional apparatus, and there is a difficulty in that a malfunction in the evaporated fuel purge system, due to a problem in the fuel tank or a clogging of the vapor passage or a connecting pipe separation therein, is not suitably detected.